<script>   
  function Customer() {   
    this.nickName = '小李';   
  }   
  // 使用箭头函数定义原型对象中的方法   
  Customer.prototype.show = () => {   
    console.log(this.nickName);   
  }   
  var cust1 = new Customer();   
   cust1.show(); // undefined   
</script> 